Plug-in coupling systems are known in various configurations. In the most simple case, there is a plug and a socket, each of them fastened to more or less elastic lines. For safety reasons, the current carrying end of the system is usually designed as a socket on the tractor. After the trailer has been coupled to the tractor, the supply lines still have to be joined together, which is usually done manually by the driver. Before uncoupling the trailer, the plug-in system has to be separated once again. If this is forgotten by accident, the coupling system or the supply lines will be torn away from each other.
Therefore, efforts have already been made to automate the joining and separating of the plug-in coupling systems and also to make this more safe. Two different approaches have basically been taken in the development of such systems.
First, there are plug-in coupling systems in which a connection between the supply lines is produced by means of a drive unit. Such an active system is specified, for example, in DE 101 55 056 A1. The known plug-in coupling system comprises a socket, which is arranged so that it can move in the fifth wheel and can be moved by its drive unit into a socket on the trailer.
To avoid damage to the socket, these systems are preferably outfitted with a sensor system, which recognizes the presence of a trailer and retracts the socket if it has been erroneously extended before any damage is caused to the coupling system during the coupling of the trailer.
As an alternative to these technically expensive plug-in coupling systems with moving components of the coupling system, there have been attempts to realize the connection of the supply lines in dependence on the presence of a trailer by means of a permanently installed plug or a permanently installed socket. Such passive systems are described in the following publications.
U.S. Pat. No. 5,060,964 discloses a fifth wheel in which the contacts are permanently arranged in the end region of the fifth wheel horns on either side of the insert hole. These interact with likewise permanent contacts on the underside of the trailer. A relative movement between the tractor contacts and the trailer contacts is prevented by a fifth wheel mounted on a pivoting base. Such a fifth wheel, in which the transmission of force between tractor and trailer is diverted in point-like manner via the pivoting base into the conductor frame of the tractor, can hardly be installed in present day tractors without considerable expense in the form of reinforcements on the tractor. Furthermore, the structural height of the fifth wheel is substantially further increased, which will in no way be welcome to the automobile makers and trucking companies, since the cargo volume will be reduced for a given maximum vehicle height.
Moreover, it has been shown in practice that the contacts due to their exposed position in the end region of the fifth wheel horns often get damaged in the coupling process due to the king pin not being exactly situated in the insert hole, so that the entire coupling system can no longer be used.
Another prior art forming its own category is DE-OS 20 39 340 with an automatic electrical air coupling, which interacts with a fully automatic fifth wheel coupling to enable the coupling and uncoupling of the trailer of a road train without the driver needing to leave his cabin. The automatic electrical air coupling is realized by a two-part coupling piece, embracing the king pin, and having contact points at its end face, which interact with contact points in the front end region of the fifth wheel coupling when the trailer is being coupled. The coupling piece is configured as a plug-in connector with a support element, and the support element has means for mounting around the king pin in swiveling manner. The main drawback of this system is the high mechanical strain on the coupling piece, which is further weakened by having a number of boreholes running in the lengthwise direction to lead in the cables or compressed air lines. Another major problem is to achieve a secure contact between the coupling piece and the fifth wheel coupling in the end region, which is greased, since the grease fouls the contacts and a flow of electricity is not always guaranteed.